1. Field of the Invention
The invention relates to a circuit arrangement for detecting whether a predetermined frequency swing is exceeded by the frequency of a first signal, comprising a detector which supplies an error-indication signal if the phase shift between the first signal and a second signal, which second signal tracks the frequency of said first signal, exceeds limit values corresponding to the frequency swing.
2. Description of the Related Art
Published West German patent application DE-PS 29 39 402 describes a circuit arrangement for the demodulation of frequency-modulated signals reproduced from a disc record and for error detection in response to the instantaneous signal frequency which normally varies within a predetermined frequency swing and which exceeds said frequency swing in the event of errors. For supplying the error signal this circuit arrangement comprises an error detector coupled to a frequency demodulator. The frequency demodulator comprises a phase-locked loop with a phase detector and a voltage-controlled oscillator. The frequency-modulated signals and oscillator signals applied to the phase detector are also applied to the error detector and, if the phase difference between these signals lies outside a predetermined phase difference range, the detector will supply the error-indication signal.
The known circuit arrangement is comparatively complex because the demodulator comprises a phase-locked loop and because in parallel with the phase detector of the loop an error detector is provided to monitor the phase difference between the frequency-modulated signals and the oscillator signals.
Not only for demodulator circuits but also for other signal-processing arrangements it is desirable to have a simple and versatile circuit arrangement for detecting whether a predetermined frequency swing is exceeded.